Following the advancement of technology, the control functions of the electric wheelchair are becoming more and more advanced, so that the electric wheelchair is an indispensable means of transport for many elderly people and people with mobility impairments. However, an existing electric wheelchair is produced by assembling together molded components of fixed specifications. As such, the front-rear length and the left-right width of the seat of the existing electric wheelchair are fixed and cannot be altered. If a user requires a longer or wider seat, the entire seat mechanism must be removed and replaced with a custom-made seat mechanism having special specifications. Thus, the existing electric wheelchair is quite inconvenient to use, and the user's purchase cost is increased.